Recovery of gastric evacuation rate in Atlantic cod Gadus morhua L surgically implanted with a dummy telemetry device

Temperature, meal size and body size effects on the gastric evacuation of rainbow trout: modelling optimum and upper thermal limits

This study examined the rate and course of gastric evacuation (GE) in rainbow trout Oncorhynchus mykiss in relation to meal size, body size and temperature. The GE experiments were performed on small (mean ± 95% C.I., 17.7 ± 0.5 cm total length), medium (22. 9 ± 0.2 cm) and large (28.3 ± 0.3 cm) rainbow trout fed meals of different sizes using commercial food pellets at water temperatures T ranging from 7.8°C to 19.2°C. Estimating the shape parameter of a general power function suggested that the square root function adequately described the GE in rainbow trout independently of meal size. The effects of total body length L and weight W on gastric evacuation rate (GER) were described by simple power functions. The square root function was further expanded by a temperature function with temperature optimum to describe the effect of temperature. The expanded square root function revealed a considerable effect of body size and temperature on the GER of rainbow trout. The GER increased exponentially with rising temperature, reached an optimum at c. 18.5°C and then declined abruptly to zero at c. 21°C. The GER of rainbow trout could thus be described by d S t d t = - 0.00152 L 0.75 e 0.08 T 1 - e 1.18 T - 20.9 S t (g h^-1 ) or d S t d t = - 0.00440 W 0.26 e 0.08 T 1 - e 0.97 T - 21.1 S t (g h^-1 ), where S_t is the current stomach content mass (g), and at post-prandial time t (h). These functions should prove useful to calculate total GE time as well as stomach fullness at different post-prandial times and therefore provide valuable information to develop optimal feeding strategies for farming of rainbow trout.

Effects of prophylactic antibiotic-treatment on post-surgical recovery following intraperitoneal bio-logger implantation in rainbow trout

Bio-logging devices can provide unique insights on the life of freely moving animals. However, implanting these devices often requires invasive surgery that causes stress and physiological side-effects. While certain medications in connection to surgeries have therapeutic capacity, others may have aversive effects. Here, we hypothesized that the commonly prescribed prophylactic treatment with enrofloxacin would increase the physiological recovery rate and reduce the presence of systemic inflammation following the intraperitoneal implantation of a heart rate bio-logger in rainbow trout (Oncorhynchus mykiss). To assess post-surgical recovery, heart rate was recorded for 21 days in trout with or without enrofloxacin treatment. Contrary to our hypothesis, treated trout exhibited a prolonged recovery time and elevated resting heart rates during the first week of post-surgical recovery compared to untreated trout. In addition, an upregulated mRNA expression of TNFα in treated trout indicate a possible inflammatory response 21 days post-surgery. Interestingly, the experience level of the surgeon was observed to have a long-lasting impact on heart rate. In conclusion, our study showed no favorable effects of enrofloxacin treatment. Our findings highlight the importance of adequate post-surgical recovery times and surgical training with regards to improving the welfare of experimental animals and reliability of research outcomes.

Effects of hypoxic exposure during feeding on SDA and postprandial cardiovascular physiology in the Atlantic cod, Gadus morhua

Some Atlantic cod in the Bornholm Basin undertake vertical foraging migrations into severely hypoxic bottom water. Hypoxic conditions can reduce the postprandial increase in gastrointestinal blood flow (GBF). This could subsequently postpone or reduce the postprandial increase in oxygen consumption (MO(2)), i.e. the SDA, leading to a disturbed digestion. Additionally, a restricted oxygen uptake could result in an oxygen debt that needs to be compensated for upon return to normoxic waters and this may also affect the ability to process the food. Long-term cardio-respiratory measurements were made on fed G. morhua in order to understand how the cardio-respiratory system of feeding fish respond to a period of hypoxia and a subsequent return to normoxia. These were exposed to 35% water oxygen saturation for 90 minutes, equivalent to the time and oxygen level cod voluntarily endure when searching for food in the Bornholm Basin. We found that i) gastric and intestinal blood flows, cardiac output and MO(2) increased after feeding, ii) gastric and intestinal blood flows were spared in hypoxia, and iii) there were no indications of an oxygen debt at the end of the hypoxic period. The magnitude and time course of the measured variables are similar to values obtained from fish not exposed to the hypoxic period. In conclusion, when cod in the field search for and ingest prey under moderate hypoxic conditions they appear to stay within safe limits of oxygen availability as we saw no indications of an oxygen debt, or negative influence on digestive capacity, when simulating field observations.